The traditional biological denitrification method in the field of water treatment is adopting nitrifying bacteria to convert ammonium nitrogen into nitrate-nitrogen under oxic conditions and then adopting heterotrophic denitrifying bacteria to convert nitrate-nitrogen into nitrogen gas, so as to realize removal of nitrogen in water. Meanwhile, the traditional biological dephosphorization method in the field of water treatment is adopting dephosphorizing bacteria firstly to release phosphorus under anaerobic conditions and then to absorb excessive phosphorus under oxic conditions, along with mass propagation of the bacteria; the phosphorus in water is then easily removed by filtering away organisms of dephosphorizing bacteria that have absorbed excessive phosphorus. Both methods of biological denitrification and biological dephosphorization involve oxic and anoxic (anaerobic) phases, therefore when applied in series or any form of combined way (namely, A2/O synchronous nitrogen and phosphorous removal process), the whole water treatment process will be very long and complicated. As is shown above, the removal of nitrogen and phosphorus depends on life activities of denitrifying bacteria and dephosphorizing bacteria respectively, however, in the course of dephosphorization, even though dissolved oxygen and carbon sources are required by both types of bacteria, their sludge age and their specific requirements for anaerobic conditions are different. Therefore, when these two types of bacteria are integrated in one process to realize synchronous removal of nitrogen and phosphorus, there may inevitably exist such problems as how to obtain balanced status between two types of bacteria in terms of sludge age and required anaerobic conditions, and how to deal with the competition for dissolved oxygen and organic substances between two types of bacteria. These problems bring great challenges to the water treatment process and make it hardly possible to achieve desirable effect in removing nitrogen and phosphorus. Besides, the process depends upon biodegradable organic substances, and when biodegradable organic substances in the water is insufficient (namely, low C/N ratio), it is necessary to add methanol and other organic substances into water to achieve good effect in nitrogen and phosphorus removal, which may further increase water treatment cost and bring about the risk of over-standard discharge of effluent COD.
In respect to the problem of nitrogen removal of wastewater with low C/N ratio, sulfur-based autotrophic denitrification processes, for example, sulfur/limestone autotrophic denitrification process (SLAD), have been developed to realize denitrifying nitrogen removal despite the absence of carbon sources. However, these processes lead to overly high concentrations of both calcium ions and sulfates in the final effluent, and poor effect in phosphorus removal as well.
In respect to the above problems existent in SLAD, a Chinese patent entitled “A Method for Removing Nitrogen and Phosphorus Using Pyrite as Biochemical Packing Material” (ZL201010524339.3) discloses a method for synchronous removal of nitrogen and phosphorus using pyrite and limestone in combination. This method, by adopting pyrite's anaerobic bio-oxidation process, integrates sulfur-based autotrophic denitrification process and chemical phosphorus removal process together. However, it results in such problems as introduction of limestone to neutralize the water for desirable pH value, high concentration of calcium ions in the water, and low efficiency in nitrogen removal. When this method is adopted to treat wastewater, it takes 5 days to fully remove 30 mg/L nitrate-nitrogen from the wastewater, and the efficiency is even worse when temperature is under 20° C.
When being adopted for synchronous removal of nitrogen and phosphorus, both SLAD and the pyrite method mentioned above introduce limestone as auxiliary material to neutralize the H+ generated in the process so that the removal process of nitrogen and phosphorus can be guaranteed. Except the function of neutralization, limestone plays no role in the whole process of synchronous removal of nitrogen and phosphorus. As limestone occupies a considerably large volume within the reactor, its introduction to the reaction system reduces the rector's volume-specific efficiency in synchronous removal of nitrogen and phosphorus.
A Chinese patent entitled “A Method for Synchronous Removal of Nitrogen and Phosphorous from the Nitrogen- and Phosphorus-containing Wastewater” (application number: 201210095370.9) discloses a method for synchronous removal of nitrogen and phosphorus in wastewater by using ferrous sulfide. This method introduces ferrous sulfide into a batch reactor to realize synchronous removal of nitrogen and phosphorus in wastewater under strict control of anaerobic conditions. When being adopted to treat a wastewater sample containing 53 mg/L nitrate-nitrogen and 1.14 mg/L phosphorus, this method, after 2 days of operation, can remove 73.6% of nitrate-nitrogen and 97.4% of phosphorous. Despite the good performance it exhibits in synchronous removal of nitrogen and phosphorous, this method is troubled with problems such as being unfit for continuous operation, requirement of carbon dioxide stripping for maintaining strict anaerobic conditions, and demand for an extra solid-liquid separation process after treatment, all of which lead to poor applicability of this method.